Aerodynamic structures can be of changeable external shape, for example to change the lift of an airfoil or to actuate an elevator unit or rudder unit. In aerodynamic structures, which have no deformable design, these functions are realized by the swivelling of jointed flaps. Aerodynamic structures with an outer skin deformable in cross section longitudinal to an air stream direction are known from U.S. Pat. No. 3,179,357, U.S. Pat. No. 3,716,202 and U.S. Pat. No. 4,349,169. U.S. Pat. No. 5,531,407 discloses an aerodynamic structure, which comprises an deformable outer skin with ribs of changeable cambering, the ribs stiffening the outer skin in cross section longitudinal to the air stream direction.
Aerodynamic structures for flying machines are subjected to a strict rule of lightweight construction, i.e. they have to be optimized with regard to their weight and to their load supporting properties. An usual construction of an airfoil fulfilling these boundary conditions comprises an outer skin, which is stiffened by ribs. Each rib is arranged longitudinal to the air stream direction. The ribs are arranged side by side at distance in the direction of main extension of the outer skin. The single ribs can consist of plates with border regions, which form wraparound frames. The outer skin is mounted on the frame of the ribs and firmly connected to the ribs. Thus, a sufficient structural stability results, i.e. sufficient load supporting properties of the whole airfoil at low weight.